function momFruiltCollision(st) {
	for (var i = 0; i < fruit.num; i++) {
		if (fruit.alive[i]) {
			//判断距离
			var l = calLength2(fruit.x[i]+fruit.long[i],fruit.y[i],mom.x,mom.y);
			//l是平方值,说明距离小于30
			if (l < 1800) {
				fruit.up(i,st);
			}
		}
	}
}